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i • If a well extends below 50 ft, centralizers should be installed at 50 ft and every 50 ft thereafter except within screened interval and bentonite seal. Centralizer material will be PVC, PTFE, or stainless steel. Centralizer material should be of the same material as the well screen. • Cut the riser with a pipe cutter approximately 2-2.5 ft above grade. All pipe cuts MUST be square to ensure that the elevation between the highest and lowest point of the well casing is-less than or equal to 0.02 ft. Notch, file, or otherwise scribe a f' permanent reference point on the top of the casing. �,, • If a flush-mounted well is required at a given location, an,internal pressure cap must be used to ensure that rainwater cannot pool around the wellhead and enter the well through the cap. • When the well is set to the bottom ofthehole, temporarily,place a cap on top of the pipe Pi e to keep the well interior clean. • Place the appropriate filter pack. Monitor the rise annulus with a weighted tape to assure that bridging is not occurring._ • After the pack is in place,wait three to five minutes for the material to settle, tamp and level a capped PVC pipe, and check its depth with a weighted steel tape. • Install the bentonite seal (2 ft to 5 ft thick)by dropping bentonite pellets into the hole gradually. If the well is deeper than 30 feet, a tremie pipe should be used to place either bentonite pellets or slurry. • Wait for the pellets to hydrate and swell. Hydration times will be determined by field test or by manufacturer's instructions. :Normally this will be 30 to 45 minutes. Document the hydration time in the field notebook. If the pellets are above the water level in the hole,add several buckets of clean water to the boring. Document the amount of water added to the hole. • 'Mix an appropriate cement-bentonite slurry. Be sure the mixture is thoroughly mixed g Y and as thick as is practicable. • Lower a side discharge tremie pipe into the annulus to the level of the pellet seal. f • Pump the grout slurry into the annulus,while withdrawing the tremie pipe and +• temporary casing. • Continue the grout fill to the ground surface. Seat the protective casing in the grout, G allowing no more than 0.2 ft between the top of the well casing and the bottom of the protective casing cap. Lock the cap. Page 8 of 9 well—install—SOP MONITORING WELL INSTALLATION February 2005 • I